Low-reflective thin-film substrate

ABSTRACT

A low-reflective thin-film substrate comprising a transparent glass substrate having formed by sputtering a thin film in multilayer containing no chromium series component and made up of at least one kind of Ni, Fe, Co, Mo, W, Ta, Cu, and Nb as a main constituent form or as an alloy thereof, the thin film having a minimum reflectivity of 0.5% or lower and the optical density of at least 4 or having a minimum reflectivity of 0.1% or lower, a maximum reflectivity of 2.0% or lower, an average reflectivity of 0.3% or lower, and an optical density of at least 4.0, in the visible light region.  
     The low-reflective thin-film substrate is useful as a black matrix for a color filter substrate of a liquid crystal panel, etc., and is free from an environmental pollution caused by the use of a chromium component as the target material.

FIELD OF THE INVENTION

[0001] The present invention relates to a low-reflective thin-filmsubstrate. More specifically, the present invention relates to alow-reflective metal•alloy system thin-film substrate which is used inthe fields relating to an optical thin film having a light shieldingproperty and a light reflection preventing property, such as, forexample, a black matrix particularly useful for the production of acolor filter substrate for a liquid crystal panel and a projector frameuseful for the production of a projector.

BACKGROUND OF THE INVENTION

[0002] A color liquid crystal panel is utilized over a wide field indisplay devices of information instruments, etc., and with the progressof the recent information-oriented society, the development aiming at alarger picture and a higher precision has been made.

[0003] In such a color liquid crystal panel, to increase the contrast ofthe picture and to sharpen the displayed picture by increasing thecoloring effect, each black matrix showing a less reflectance and havinga good light-shielding property is disposed between each color filterpixels of red (R), green (G), and blue (B).

[0004] Hitherto, the black matrix is produced by applying patterning byetching using a known photolithographic technique to a low-reflectivethin-film substrate formed by laminating metal layers, etc., bysputtering metal targets such as chromium, etc. As such a laminatedlow-reflective thin-film substrate, a low-reflective thin-film substrateformed by laminating a chromium oxide layer and a chromium metal layeris known.

[0005] In this case, because the reflectivity is restrained by theinterference of light by the laminated layers in multilayer and thelaminated layers included a chromium metal layer having a highreflectivity and a less transmissibility of light, the laminatedlow-reflective thin-film substrate has a light-shielding function.

[0006] Also, in regard to the black matrix, it has been required tolower the reflectivity for easily seeing images by restraining thereflection images such as a face, etc., and the background onto adisplay panel as completely as possible and also to keep the opticaldensity of the black matrix above a definite level because if the lightfrom a back light in the inside of the panel transmits, the color tonedoes not become clear.

[0007] From the view point, to produce a low-reflective thin-filmsubstrate having a low reflectivity and a definite optical density, amethod of forming film(s) by sputtering a material containing chromiummetal as a target has hitherto been known and utilized as a typicaltechnique.

[0008] However, in general, chromium having other valences thanhexavalence has less toxicity but chromium having a hexa-valence has astrong toxicity and there is a problem of causing an environmentalpollution. Thus, recently, in view of public opinion, there is atendency of restraining the use of chromium metal in the production ofliquid crystal panels and a low-reflective thin-film substratecontaining no chromium component has been required.

[0009] Furthermore, although in a known low-reflective chromium thinfilm, the minimum reflectivity is 0.5% or lower (the wavelength is about600 nm) and the optical density is 4.0 or higher, it is the presentsituation that the average reflectivity (the value obtained by summingup the reflectivities per an interval of, for example, 1 nm inwavelength and dividing the sum up value by the number of the measuredpoints) in a wavelength region of from 400 to 700 nm (almost the wholeregion of visible light) is 1.5% or higher and the maximum reflectivityexceeds 5%. The reflectivity is confirmed by measuring an aluminum thinfilm as a reference using a microspectroscope, OSP-SP 200, trade name,manufactured by Olympus Optical Company Limited and does no contain thereflectivity from a glass surface.

[0010] In general, in a low-reflective thin-film substrate wherein theminimum reflectivity is 0.5% or lower and the maximum reflectivityexceeds 5%, the reflected color is influenced by the wavelength showingthe maximum reflectivity. In fact, for example, in the wavelength regionof from 400 to 700 nm, when the wavelength showing the maximumreflectivity is in a short wavelength side of 400 nm (near), a bluishpurple color is emphasized in the reflected color and when thewavelength showing the maximum reflectivity is in a long wavelength sideof 700 nm (near), a red color is emphasized in the reflected color.

[0011] When such a low-reflective thin-film substrate is used as aprojector frame, there is a fault that the frame projected onto a screenbecomes bluish purple or red.

[0012] Also, it is proposed to use a resin as a low-reflective thin-filmsubstrate but in the case of using the resin, because the resin isinferior in the points of the light resistance and the heat resistanceas compared with the case of using inorganic materials, there is aproblem that the optical characteristics are greatly deteriorated by anintense light source.

[0013] Accordingly, recently, the realization of a low-reflectivethin-film substrate which does not cause an environmental problem ascaused in the case of a chromium substrate as described above as well ashas a low reflectivity in almost all the wavelength region of visiblelight and also is excellent in the light resistance has been required.

SUMMARY OF THE INVENTION

[0014] The present invention has been made for solving theabove-described problems in the conventional techniques.

[0015] That is, according to a first aspect of the present invention,there is provided a low-reflective thin-film substrate comprising atransparent glass substrate having formed thereon by sputtering a thinfilm made of at least one kind of Ni, Fe, Co, Mo, W, Ta, and Nb andhaving a minimum reflectivity of 0.5% or lower and an optical density ofat least 4 in the visible light region.

[0016] Also, according to a second aspect of the present invention,there is provided a low-reflective thin-film substrate comprising atransparent glass substrate having formed thereon by sputtering a thinfilm in multilayer containing no Cr and made of at least one kind of Ni,Fe, Co, Mo, W, Ta, Cu, and Nb.

[0017] Furthermore, according to a third aspect of the presentinvention, there is provided a low-reflective thin-film substratecomprising a transparent glass substrate having formed thereon bysputtering an aluminum series thin film having a minimum reflectivity of0.5% or lower and an average reflectivity of 2% or lower in a visiblelight region.

[0018] Also, according to a fourth aspect of the present invention,there is provided a low-reflective thin-film substrate of the thirdaspect wherein the optical density of the thin film is at least 4.

[0019] Still further, according to a fifth aspect of the presentinvention, there is provided a low-reflective thin-film substratecomprising a transparent glass substrate having formed thereon bysputtering a thin film or a thin film in multilayer containing no Cr andmade of aluminum as a main constituent.

[0020] Also, according to a sixth aspect of the present invention, thereis provided a low-reflective thin-film substrate comprising atransparent glass substrate having formed thereon by sputtering a thinfilm having a minimum reflectivity of 0.1% or lower, a maximumreflectivity of 2.0% or lower, and an average reflectivity of 0.3% orlower in the visible light region.

[0021] Furthermore, according to a seventh aspect of the presentinvention, there is provided a low-reflective thin-film substrate of thesixth aspect wherein the optical density of the thin film is at least4.0.

[0022] Still further, according an eighth aspect of the presentinvention, there is provided a low-reflective thin-film substratecomprising a transparent glass substrate having formed thereon bysputtering a thin film of Ta in multilayer.

[0023] Also, according to a ninth aspect of the present invention, thereis provided a low-reflective thin-film substrate of the eighth aspectwherein the thin film of Ta contains at least one kind of Ni, Fe, Co, W,Nb, Cu, Ti, Zr, and Sn.

[0024] Moreover, according to a tenth aspect of the present invention,there is provided a low-reflective thin-film substrate of the first toninth aspects wherein sputtering is carried out under a gas atmosphereof at least one kind of an inert gas, an oxygen gas, and a carbon oxidegas in a vacuum film-forming apparatus.

[0025] That is, according to the present invention, the low-reflectivethin-film substrate is obtained without using a chromium series metal inthe production process thereof as well as the characteristics such asthe optical density, the reflectivity, etc., thereof are by no meansinferior to the characteristics of the case of forming the thin filmusing a chromium series metal and further, the results that thereflectivity is low in the wide wavelength region of visible light andthe form of the spectral reflectivity curve is flattened in a wide rangeare also obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a schematic cross-sectional view of a double layerstructure illustrating an embodiment of the low-reflective thin-filmsubstrate of the present invention,

[0027]FIG. 2 is a graph illustrating the relation of the wavelength oflight and the reflectivity in a low-reflective thin-film substrate,wherein curve A is the curve by the low-reflective nickel-iron alloythin-film substrate of Example 1 and curve B is the curve by alow-reflective chromium thin-film substrate for comparison,

[0028]FIG. 3 is a schematic cross-sectional view of a three-layerstructure illustrating another embodiment of the low-reflectivethin-film substrate of the present invention,

[0029]FIG. 4 is a graph illustrating the wavelength of light and thereflectivity in a low-reflective thin-film substrate, wherein curve C isthe curve by the low-reflective nickel-molybdenum alloy thin-filmsubstrate of Example 2 and curve D is the curve by the low-reflectivenickel-tungsten alloy thin-film substrate of Example 3,

[0030]FIG. 5 is a graph illustrating the relation of the wavelength oflight and the reflectivity in a low-reflective thin-film substrate,wherein curve E is the curve by the low-reflective nickel-copper alloythin-film substrate of Example 4,

[0031]FIG. 6 is a graph illustrating the relation of the wavelength oflight and the reflectivity in a low-reflective thin-film substrate,wherein curve F is the curve by the low-reflective aluminum thin-filmsubstrate of the present invention and curve G is the curve by alow-reflective chromium thin-film substrate for comparison,

[0032]FIG. 7 is graphs simply illustrating the wavelength-refractiveindex characteristics obtained by forming a single layer of each of thelayers of the low-reflective aluminum thin-film substrate of the presentinvention on a transparent glass substrate and measuring by an opticalellipsometer, wherein (a) shows the wavelength-refractive indexcharacteristics of the first layer, (b) shows those of the second layer,and (c) shows those of the third layer,

[0033]FIG. 8 is a graph illustrating the relation of the wavelength oflight and the reflectivity in a low-reflective thin-film substrate,wherein curve H is the curve by the low-reflective tantalum thin-filmsubstrate of the present invention and curve I is the curve by alow-reflective chromium thin-film substrate for comparison, and

[0034]FIG. 9 is graphs simply illustrating the wavelength-refractiveindex characteristics obtained by forming a single layer of each of thelayers of the low-reflective tantalum thin-film substrate of the presentinvention on a transparent glass substrate and measuring an opticalellipsometer, wherein (a) shows the wavelength-refractive indexcharacteristics of the first layer, (b) shows those of the second layer,and (c) shows those of the third layer.

DETAILED DESCRIPTION OF THE INVENTION

[0035] Then, the present invention is described in detail.

[0036] As described above, the essential feature of the low-reflectivethin-film substrate of the present invention is that it is thelow-reflective thin-film substrate having the optical characteristicswhich have never been known as a low-reflective thin-film substrate andthat it does not contain chromium at all.

[0037] The low-reflective thin-film substrate of the present inventionis laminated in multilayer as a conventional low-reflective chromiumthin-film substrate and, for example, is laminated in from about 2 to 7layers. In this case, the thickness of each layer is properly selected.

[0038] In the present invention, sputtering can be practiced asso-called reactive gas sputtering and an inert gas such as nitrogen,etc., including a rare gas such as argon, etc., an oxygen gas, or acarbon oxide gas such as CO, CO₂, etc. , is shown as a typical exampleof the atmosphere for sputtering.

[0039] The target material includes iron group metals, that is, thematerials made up of at least one kind-of Ni, Fe, Co, Mo, W, Ta, and Nb,for example, typically, alloys such as Ni-Fe (Permalloy), Ni-Co, Fe-Co,Ni-Fe-Co, Ni-Mo, Ni-W, Ni-Ta, Fe-Mo, Fe-W, Fe-Nb, Ni-Cu, Ni-Mo-Ta, etc.,and metals such as Ta, Nb, etc. In sputtering wherein the targetmaterial may contain at least one kind of Cu, Ti, Zr, and Sn as anaccelerating addition component, in the case of the sputtering filmformation of two layers, it is considered to make the thickness of thefirst layer (the layer formed on a transparent glass substrate) to therange of from 30 to 60 nm and the thickness of the second layer to therange of from 70 to 160 nm, and also in the case of the sputtering filmformation of three layers, to make the thickness of the first layer tothe range of from 1 to 60 nm, the thickness of the second layer to therange of from 20 to 80 nm, and the thickness of the third layer to therange of from 80 to 150 nm.

[0040] In sputtering using as the target material an aluminum seriesmaterial, such as, typically, aluminum or a material made up of aluminumas a main constituent, which further properly contains titanium,zirconium, tantalum, hafnium, and other elements, in the case of thesputtering film formation of three layers, it is considered to make thethickness of the first layer (the layer formed on a transparent glasssubstrate) to the range of from 40 to 60 nm, the thickness of the secondlayer to the range of from 280 to 320 nm, and the thickness of the thirdlayer to the range of from 40 to 100 nm.

[0041] Also, in sputtering using as the target material Ta or a Ta alloycontaining at least one kind of Ni, Fe, Co, and W, the Ta or Ta alloyfurther contains at least one kind of Cu, Ti, Zr, and Sn, thelow-reflective thin-film substrate obtained has a light-shieldingfunction because the reflectivity is restrained by the interference oflight caused by the laminated layers in multilayer and the laminatedlayers includes a tantalum metal layer having a high reflectivity and aless transmissivity of light. In the sputtering film formation of thiscase, it is considered to make the thickness of the first layer (thelayer formed on a transparent glass substrate) to the range of from 40to 60 nm, the thickness of the second layer to the range of from 20 to50 nm, and the thickness of the third layer to the range of from 150 to200 nm.

[0042] The following Examples are intended to illustrate the presentinvention in more detail but, as a matter of course, not to limit theinvention in any way.

EXAMPLE Example 1

[0043] A transparent glass substrate (thin plate glass, 1737 material,made by Corning Glass Works) was used as a transparent substrate andafter washing to obtain a clean surface thereof, the transparent glasssubstrate was mounted on a batch-type reactive gas sputtering apparatussuch that the glass substrate faced a sputtering target made up of anickel (80 wt. %)-iron (20 wt. %) alloy.

[0044] The sputtering apparatus was evacuated until the inside pressurebecame 2.0×10⁻⁶ Torr or lower, then 360 sccm of a nitrogen gas and 40sccm of an oxygen gas were introduced into the sputtering apparatus, andsputtering was carried out in the atmosphere at a sputtering electricpower of 5 kW for 7.5 minutes to form a layer on a transparent glasssubstrate (3) as shown in FIG. 1 of the accompanying drawing. Also, inthis case, the substrate was not heated at sputtering. That is, by thereactive gas sputtering using the above-described nickel-iron alloy asthe target, a first layer (1) was formed on the transparent glasssubstrate (3) at a layer thickness of 44 nm.

[0045] Then, 200 sccm of an argon gas was introducing into thesputtering apparatus and sputtering was carried out in the atmosphere ofa film-forming pressure of 1.7±0.3 mTorr at a sputtering electric powerof 5 kw for about 12 minutes without heating the substrate. By thereactive gas sputtering using the above-described nickel-iron alloy asthe target, a second layer (2) was formed on the first layer (1) at athickness of 110 nm.

[0046] The total film-thickness of the low-reflective thin-filmsubstrate (4) of a double-layer structure obtained was about 154 nm.Also, the optical density thereof was 4.3, which shows the excellentlight-shielding property of the low-reflective thin-film substrate.

[0047] Also, the relation of the wavelength of light and thereflectivity in the low-reflective thin-film substrate was as shown bythe curve A of FIG. 2, that is, the maximum reflectivity in the visiblelight region (i.e., the wavelength region of from 400 to 700 nm ) was0.05% or lower and the maximum reflectivity was 6.3% or lower when thewavelength was about 600 nm, which were very low. Also, in this case,the reflectivity was measured using a microspectroscope, OSP-SP 200,manufactured by Olympus Optical Company Limited using an aluminum thinfilm as a reference and did not include the reflectivity from a glasssurface and so forth.

[0048] For comparison, the reflectivity curve B of a low-reflectivethin-film chromium substrate obtained using a chromium metal as thesputtering target was shown together in FIG. 2.

[0049] As is clear from the comparison of the curve A with the curve Bof FIG. 2, the low-reflective thin-film substrate by the presentinvention is by no means inferior to the low-reflective chromiumthin-film substrate in regard to the optical characteristics such as theminimum reflectivity, etc.

[0050] In addition, when the above-described first layer is formed as amultilayer structure by properly changing the kind of the introducinggases and the flow ratio of the introducing gases, the similarlow-reflective thin-film substrate is obtained.

[0051] As the target material, it was confirmed that in addition to theabove-described nickel-iron alloy, a nickel-molybdenum (28 wt. %) alloy,a nickel-tungsten (19.1 wt. %) alloy, nickel alloys containing copperand other elements, etc., were similarly useful for producing thelow-reflective thin-film substrates.

Example 2

[0052] A film formation was carried out using a sputtering target madeof a nickel (72 wt. %) -molybdenum (28 wt. %) alloy and also using thetransparent glass substrate and the sputtering apparatus as in Example1.

[0053] The sputtering apparatus was evaluated until the inside pressurebecame 2.0×10⁻⁶ Torr or lower and then, after introducing therein 300sccm of a nitrogen gas and 100 sccm of an oxygen gas, sputtering wascarried out in the atmosphere of the film-forming pressure of about 2.3mTorr at a sputtering electric power of 7.0 kW for 615 seconds. In thiscase, the temperature of the substrate was about 200° C. By the reactivegas sputtering using the above-described nickel-molybdenum alloy as thetarget, a first layer (11) was formed on a transparent glass substrate(3) at a thickness of 41 nm as shown in FIG. 3.

[0054] Then, 240 sccm of an argon gas, 160 sccm of a nitrogen gas, and40 sccm of an oxygen gas were introducing into the sputtering apparatusand sputtering was carried out in the atmosphere of a film-formingpressure of about 3.3 mTorr at a sputtering electric power of 8.3 kW for280 seconds. By the reactive gas sputtering using the above-describednickel-molybdenum alloy as the target, a second layer (12) was formed onthe first layer (11) at a thickness of 41 nm.

[0055] Then, successively, 200 sccm of a nitrogen gas was introducedinto the sputtering apparatus and sputtering was carried out in theatmosphere of the film-forming pressure of about 1.2 mTorr at asputtering electric power of 8.3 kW for 1330 seconds. By the reactivegas sputtering using the above-described nickel-molybdenum alloy as thetarget, a third layer (13) was formed on the second layer (12) at athickness of 115 nm.

[0056] In addition, in place of using 200 sccm of the nitrogen gas usedfor forming the third layer (13), an argon gas or a mixed gas of anargon gas with a nitrogen gas or an oxygen gas can be introduced.

[0057] The total film thickness of a low-reflective thin-film substrate(14) of a three-layer structure obtained was 197 nm and the opticaldensity thereof was 4.1, which showed the excellent light-shieldingproperty of the low-reflective thin-film substrate.

[0058] Also, the relation of the wavelength of light and thereflectivity in the low-reflective thin-film substrate obtained is asshown in the curve C of FIG. 4, that is, the minimum reflectivity in thevisible light region (i.e., the wavelength region of from 400 to 700 nm)was 0.05% or lower when the wavelength was 600 nm and the maximumreflectivity thereof was 4.7%, which were very low.

Example 3

[0059] A film formation was carried out using the sputtering target madeup of a nickel (80.9 wt. %) -tungsten (19.1 wt. %) alloy and using thetransparent glass substrate and the sputtering apparatus as used inExample 1.

[0060] The sputtering apparatus was evaluated until the inside pressurebecame 2.0×10⁻⁶ Torr or lower and then, after introducing 340 sccm of anitrogen gas and 60 sccm of an oxygen gas into the sputtering apparatus,sputtering was carried out in the atmosphere of the film-formingpressure of about 2.3 mTorr at a sputtering electric power of 8.3 kW for195 seconds. Also, in this case, the temperature of the substrate wasabout 200° C. By the reactive gas sputtering using the above-describednickel-tungsten alloy as the target, a first layer (11) was formed on atransparent glass (3) at a thickness of 17 nm as shown in FIG. 4.

[0061] Then, 120 sccm of an argon gas, 240 sccm of a nitrogen gas, and40 sccm of an oxygen gas were introduced into the sputtering apparatusand sputtering was carried out in the atmosphere of the film-formingpressure of about 2.5 mTorr at a sputtering electric power of 8.3 kW for238 seconds. By the reactive gas sputtering using the above-describednickel-tungsten alloy as the target, a second layer (12) was formed onthe first layer (11) at a thickness of 32 nm.

[0062] Then, 200 sccm of an argon gas was introduced into the sputteringapparatus and sputtering was carried out in the atmosphere of afilm-forming pressure of about 2.0 mTorr at a sputtering electric powerof 8.3 kW for 400 seconds. By the reactive gas sputtering using theabove-described nickel-tungsten alloy as the target, a third layer (13)was formed in the second layer (12) at a thickness of 100 nm.

[0063] The total film thickness of a low-reflective thin-film substrate(14) of a three-layer structure obtained was 149 nm and the opticaldensity thereof was 4.2, which showed the excellent light-shieldingproperty of the low-reflective thin-film substrate.

[0064] Also, the relation of the wavelength of light and thereflectivity in the low-reflective thin-film substrate obtained is asshown in the curve D of FIG. 4, that is, the minimum reflectivity in thevisible light region (i.e., the wavelength region of from 400 to 700 nm)was 0.12% or lower when the wavelength was 610 nm and the maximumreflectivity thereof was 6.88%, which were very low.

Example 4

[0065] A film formation was carried out using the sputtering target madeup of a nickel (55 wt. %) -copper (45 wt. %) alloy and using thetransparent glass substrate and the sputtering apparatus as used inExample 1.

[0066] The sputtering apparatus was evaluated until the inside pressurebecame 2.0×10⁻⁶ Torr or lower and then, after introducing 240 sccm of anitrogen gas , 80 sccm of an oxygen gas, and 80 sccm of an argon gasinto the sputtering apparatus, sputtering was carried out in theatmosphere of the film-forming pressure of about 2.5 mTorr at asputtering electric power of 6.0 kW for 330 seconds. In this case, thetemperature of the substrate was about 200° C. Also, in this case, bythe reactive gas sputtering using the above-described nickel-copperalloy as the target, a first layer (1) was formed on a transparent glass(3) at a thickness of 45 nm as shown in FIG. 1 of the accompanyingdrawing.

[0067] Then, 140 sccm of an argon gas and 60 sccm of a nitrogen gas wereintroduced into the sputtering apparatus and sputtering was carried outin the atmosphere of the film-forming pressure of about 2.0 mTorr at asputtering electric power of 8.3 kW for 550 seconds. By the reactive gassputtering using the above-described nickel-copper alloy as the target,a second layer (2) was formed on the first layer (1) at a thickness of140 nm.

[0068] The total film thickness of a low-reflective thin-film substrate(4) of the double-layer structure obtained was 185 nm and the opticaldensity thereof was 4.1, which showed the excellent light-shieldingproperty of the low-reflective thin-film substrate.

[0069] Also, the relation of the wavelength of light and thereflectivity in the low-reflective thin-film substrate obtained is asshown in the curve E of FIG. 5, that is, the minimum reflectivity in thevisible light region (i.e., the wavelength region of from 400 to 700 nm)was 0.11% or lower when the wavelength was 610 nm and the maximumreflectivity thereof was 6.06%, which were very low.

Example 5

[0070] A transparent glass substrate (thin plate glass, 1737 material,made by Corning Glass Works) was used as a transparent substrate andafter washing to obtain a clean surface thereof, the transparent glasssubstrate was mounted on a batch-type reactive gas sputtering apparatussuch that the glass substrate faced a sputtering target of a metal(containing 4 wt. % titanium) made up of aluminum as a main constituent.

[0071] The sputtering apparatus was evacuated until the inside pressurebecame 0.1 mTorr or lower, then 140 sccm of an argon gas and 60 sccm ofa nitrogen gas were introduced into the sputtering apparatus, andsputtering was carried out in the atmosphere at a sputtering electricpower of 10 kW for 10 minutes to form a film on a transparent glasssubstrate (3) as shown in FIG. 3 of the accompanying drawing. In thiscase, the film-forming pressure was kept at 1.8±0.3 mTorr. Also, in thiscase, the substrate was not heated at sputtering.

[0072] Then, by the reactive gas sputtering using as the target theabove-described metal made up of aluminum as a main constituent, a firstlayer (11) was formed on the transparent glass substrate (3) at athickness of 48 nm.

[0073] Then, 160 sccm of an argon gas and 40 sccm of a nitrogen gas wereintroducing into the sputtering apparatus and sputtering was carried outin the atmosphere of a film-forming pressure of 1.7±0.3 mTorr at asputtering electric power of 10 kW for about 15 minutes without heatingthe substrate. By the reactive gas sputtering using as the target theabove-described metal made up of aluminum as a main constituent, asecond layer (12) was formed on the first layer (11) at a thickness of293 nm.

[0074] Then, 200 sccm of an argon gas was introducing into thesputtering apparatus and sputtering was carried out in the atmosphere ofthe film-forming pressure of 2.1±0.3 mTorr at a sputtering electricpower of 10 kW for about 3 minutes without heating the substrate. By thereactive gas sputtering using as the target the metal made up ofaluminum as a main constituent, a third layer (13) was formed on thesecond layer (12) at a thickness of 51 nm.

[0075] The total average thickness of a low-reflective thin-filmsubstrate (14) thus obtained was about 392 nm. Also, the optical densitythereof was 5.1, which showed the excellent light-shielding property ofthe low-reflective thin-film substrate.

[0076] Also, the relation of the wavelength of light and thereflectivity in the low-reflective thin-film substrate was as shown bythe curve F of FIG. 6, that is, the minimum reflectivity in the visiblelight region (i.e., the wavelength region of 400 to 700 nm) was 0.1% orlower and the average reflectivity in the visible light region was 2% orlower.

[0077] For comparison, the reflectivity curve G of a low-reflectivechromium thin-film substrate obtained using a chromium metal as thesputtering target was shown together in FIG. 6.

[0078] As is clear from the comparison of the curve F with the curve Gin FIG. 6, the low-reflective aluminum thin-film substrate of thepresent invention is by no means inferior to the low-reflective chromiumthin-film substrate in regard to the minimum reflectivity, and also, theaverage reflectivity of the low-reflective aluminum thin-film substrateof the present invention is 0.93%, which is considerably lower than 1.9%of that of the low-reflective chromium thin-film substrate.

Example 6

[0079] Each single layer of the layers from the first layer to the thirdlayer of the low-reflective aluminum thin-film substrate of Example 5was formed on each transparent glass substrate and the refractive indexthereof was evaluated using a spectral ellipsometer made by SOPRA Co. Anexample of the result thereof was shown in FIG. 7.

Example 7

[0080] A transparent glass substrate (thin plate glass, 7059 material,made by Corning Glass Works) was used as a transparent substrate andafter washing to obtain a clean surface thereof, the transparent glasssubstrate was mounted on a batch-type reactive gas sputtering apparatussuch that the glass substrate faced a sputtering target made up of atantalum (Ta). In addition, the transparent glass substrate was notheated.

[0081] The sputtering apparatus was evacuated until the inside pressurebecame 2.0×10⁻⁶ Torr or lower, then 200 sccm of an argon gas and 200sccm of an oxygen gas were introduced into the sputtering apparatus, andsputtering was carried out in the atmosphere of the pressure of 2.2×10⁻³Torr at a sputtering electric power of 8.3 kW for about 27 minutes. Bythe reactive gas sputtering using tantalum as the target, a first layer(11) was formed on a transparent glass substrate (3) at a thickness ofabout 51 nm as shown in FIG. 3 of the accompanying drawing.

[0082] Then, 240 sccm of an argon gas and 160 sccm of a nitrogen gaswere introducing into the sputtering apparatus and sputtering wascarried out in the atmosphere of 2.3×10⁻³ Torr at a sputtering electricpower of 8.3 kW for about 5 minutes. By the reactive gas sputteringusing tantalum as the target, a second layer (12) was formed on thefirst layer (11) at a thickness of about 35 nm.

[0083] Then, 200 sccm of an argon gas was introduced into the sputteringapparatus and sputtering was carried out in the atmosphere of 1.5×10⁻³Torr at a sputtering electric power of 8.3 kW for about 35 minutes. Bythe reactive gas sputtering using tantalum as the target, a third layer(13) was formed on the second layer (12) at a thickness of about 170 nm.

[0084] The total film thickness of a low-reflective thin-film substrate(14) of a three-layer structure obtained was about 256 nm. The opticaldensity thereof was 4.2 and thus the low-reflective thin-film substrateobtained was excellent in the light-shielding property.

[0085] Also, the relation of the wavelength of light and thereflectivity in the low-reflective thin-film substrate was as shown inthe curve H of FIG. 8, that is, the minimum reflectivity thereof was0.01% or lower, the maximum reflectivity was 1.53%, and the averagereflectivity was 0.24% or lower in the measured wavelength in thevisible light region of from 400 to 700 nm, and thus the low-reflectivethin-film substrate having a very low reflectivity was obtained.

[0086] For comparison, the reflectivity curve I of a low-reflectivechromium thin-film substrate obtained using a chromium metal as thesputtering target is shown together in FIG. 8.

[0087] As is clear from the comparison of the curve H with the curve Iin FIG. 8, the reflectivity of the low-reflective tantalum thin-filmsubstrate of the present invention is low in a wide range of themeasured wavelengths as compared with the low-reflective chromiumthin-film substrate. In particular, it can be seen that thereflectivities in the wavelength of about 400 nm and the wavelength ofabout 700 nm are clearly low in the low-reflective tantalum thin-filmsubstrate of the present invention as compared with the comparativelow-reflective chromium thin-film substrate.

[0088] The reflective characteristic values of the low-reflectivethin-film substrates are shown in Table 1 below. The range of themeasured wavelength is from 400 nm to 700 nm. TABLE 1 Kind of low-Reflectivity of each reflective thin-film Minimum measured wavelengthAverage substrate (target reflectivity (%) reflectivity material used)(%) 400 nm 700 nm (%) Chromium ≦0.01 6.10 2.08 1.76 Tantalum ≦0.01 1.530.15 0.23

[0089] In addition, it could be confirmed that in the low-reflectivetantalum thin-film substrate of the present invention, the reflectivitywhich became maximum when the wavelength was 400 nm could be lowered to1.0% or lower by delicately changing the total thickness of the firstlayer and the second layer and the layer ratio of these layers. On theother hand, in the case of the low-reflective chromium thin-filmsubstrate, whereas when the reflectivity in the wavelength of 400 nm waslowered, the reflectivity in the wavelength of 700 nm became high,whereby the average reflectivity was not lowered too much.

[0090] It was similarly confirmed that as the target material, inaddition to tantalum shown in the above-described Example, tantalumalloys containing at least one of nickel, iron, cobalt, tungsten,copper, and other elements were also useful.

Example 8

[0091] Each single layer of the layers from the first layer to the thirdlayer of the low-reflective tantalum thin-film substrate of Example 7was formed on each transparent glass substrate and the refractive indexthereof was evaluated using a spectral ellipsometer made by SOPRA Co. Anexample of the results was shown in FIG. 9.

[0092] As described above, according to the present invention, alow-reflective thin-film substrate which meets with the tendency ofself-discipline the use of a chromium metal in the production process ofcolor liquid crystals, projectors, etc., does not contain chromiumcomponents, and has the characteristics such as the optical density, thereactivity, etc., that are by no means inferior to the characteristicsof the low-reflective thin-film substrate prepared using a chromiumseries metal is provided. Furthermore, the low-reflective thin-filmsubstrate of the present invention has the low reflectivity in a widewavelength region of visible light, has the result that the form of thespectral reflectivity curve is flattened in a wide range, and thus theutilization thereof as the thin-film substrate having not only thefunction same as conventional low-reflective thin-film substrates butalso having higher functions has been expected.

What is claimed is:
 1. A low-reflective thin-film substrate comprising atransparent glass substrate having formed thereon by sputtering a thinfilm made up of at least one kind of Ni, Fe, Co, Mo, W, Ta, and Nbhaving a minimum reflectivity of 0.5% or lower and an optical density ofat least 4 in the visible light region.
 2. A low-reflective thin-filmsubstrate of claim 1, wherein the thin film is formed in multilayer onthe transparent glass substrate by sputtering a target materialcontaining no chromium component and made up of at least one kind of Ni,Fe, Co. Mo, W, Ta, and Nb.
 3. A low-reflective thin-film substrate ofclaim 1 or 2, wherein the thin film is formed by sputtering under a gasatmosphere of at least one kind of an inert gas, an oxygen gas, and acarbon oxide gas in a vacuum film-forming apparatus.
 4. A low-reflectivethin-film substrate of claim 1 to 3, wherein an alloy of at least onekind of Ni, Fe, and Co and at least one kind of Mo, W, Ta, and Nb isused as the target material.
 5. A low-reflective thin-film substrate ofclaim 1 to 3, wherein an alloy of at least two kinds of Ni, Fe, and Cois used as the target material.
 6. A low-reflective thin-film substrateof claim 2 to 5, wherein the target material contains at least one kindof Cu, Ti, Zr, and Sn.
 7. A low-reflective thin-film substratecomprising a transparent glass substrate having formed thereon bysputtering an aluminum series thin film having a minimum reflectivity of0.5% or lower and an average reflectivity of 2% or lower in the visiblelight region.
 8. A low-reflective thin-film substrate of claim 7,wherein the optical density of the aluminum sries thin film is at least4.
 9. A low-reflective thin-film substrate of claim 7 or 8, wherein thealuminum series thin film is formed on the transparent glass substrateby sputtering of the target material containing no chromium componentand made up of aluminum as a main constituent.
 10. A low-reflectivethin-film substrate of claim 7 to 9, wherein the aluminum series thinfilm is formed in multilayer.
 11. A low-reflective thin-film substrateof claim 7 to 10, wherein the thin film is formed by sputtering under agas atmosphere of at least one kind of an inert gas, an oxygen gas, anda carbon oxide gas in a vacuum film-forming apparatus.
 12. Alow-reflective thin-film substrate comprising a transparent glasssubstrate having formed thereon by sputtering a thin film having aminimum reflectivity of 0.1% or lower, a maximum reflectivity of 2.0% orlower, and an average reflectivity of 0.3% or lower in the visible lightregion.
 13. A low-reflective thin-film substrate of claim 12, whereinthe optical density of the thin film is at least 4.0.
 14. Alow-reflective thin-film substrate of claim 12 or 13, wherein Ta isformed on the transparent glass substrate in multilayer as the thin filmby sputtering of a target material.
 15. A low-reflective thin-filmsubstrate of claim 12 to 14, wherein the thin film is formed bysputtering under a gas atmosphere of at least one kind of an inert gas,an oxygen gas, and a carbon oxide gas in a vacuum film-formingapparatus.
 16. A low-reflective thin-film substrate of claim 12 to 15,wherein a Ta alloy containing at least one kind of Ni, Fe, Co, W, Nb,Cu, Ti, Zr, and Sn is used as the target material.